The overarching goal of this Program is to understand the molecular mechanisms that regulate cell activation. Activation of lymphocytes through specific recognition of antigen poses narrowly balanced benefits and risks, and hence is subject to tight regulation. We know that some signals serve to modulate or terminate activation, while other signals induce cell unresponsiveness or death. The molecular mechanisms underlying the regulatory processes with different outcomes are unknown and largely undefined. The Program consists of five highly interactive projects involving six investigators, from five different departments of the University. These investigators bring innovative technology and incisive ideas to bear on the problem of lymphocyte activation and its regulation. The five projects cover a range of stimuli, cues and outcomes that result in various states of T cell activation or unresponsiveness, from the initial events of antigen recognition to the regulation of transcription. The projects cover a biological scale from nano-scale molecular interactions to whole cell and animal models. The program addresses the following areas: 1) Influence of TCR spatial organization on T cell responses, 2) Altered molecular architecture at the Immunological Synapse and T cell anergy, 3) Sprouty 1 as a novel inhibitor of T cell activation, 4) Regulation of calcium signaling in T cells by TFII-I, 5) Regulation of NF-kB by TCR and costimulatory signaling. These five projects support the overall goal of understanding the molecular mechanisms regulating cell activation. The program has developed out of years of interaction among a core group of investigators who in the last two years have been joined by new colleagues. Interactions between investigators are flourishing. The extent of synergy between group members is apparent from the detailed project descriptions. We want to understand the mechanisms of T cell responses to antigen. Understanding these mechanisms will lead to ways of turning up, or turning off immune responses that are helpful or harmful.